Multiplex reciprocating pumps are generally used to pump high pressure fracturing fluids into wells for recovery of oil and gas trapped in shale formations and the like. Typically, these pumps have two sections, a power end which is coupled to a diesel engine and transmission that drives the pump and plungers in the fluid ends in which a mix of water, sand and chemicals are pressurized up to 15,000 psi or more.
These multiplex reciprocating pumps are commonly in the form of triplex pumps having three fluid cylinders and quintuplex pumps that have five cylinders. It will be appreciated, however, that the present disclosure has application to pumps which can utilize the features thereof in forms other than the triplex and quintuplex pumps. The fluid ends of these pumps typically comprise a single block having cylinders bored therein and are commonly referred to as monoblock fluid ends or an assembly of individual bodies with cylinders, referred to as modular fluid ends.
The pumping cycle of a fluid end is composed of two stages, a suction cycle during which a piston moves outward in a bore, thereby lowering the fluid pressure in the inlet to a fluid end and a discharge cycle during which the plunger moves forward in the plunger bore, thereby progressively increasing the fluid pressure to a predetermined level for discharge through a discharge pipe to a well site.
Fluid ends used in well site applications for oil and gas exploration have limited service life due to fatigue crack failures. These failures are a result of operating pressures, mechanical stresses, erosion and corrosion of the internal passages which have been addressed in prior art efforts with limited success.
Discussion of the Prior Art
International Application No. PCT/IB2011/002771 (International Publication No. WO 2012 052842 A2 entitled “Fluid End Reinforced With Abrasive Resistant Insert, Coating or Lining”) describes the use of inserts in wear prone areas only and, as such, does not provide erosion, corrosion and fatigue crack protection throughout the entire flow passages in the fluid end.
U.S. Patent Publication 2008/0080994 A1, “Fluid End Reinforced With a Composite Material,” is directed to a fluid end of a reciprocating pump wherein carbon steel thin base material is formed into three tubes which are welded and then hydroformed to give a cross-like configuration. That structure is reinforced with a composite that provides some additional stress resistance and reduced weight, however, it does not utilize the inherent benefits of the originally designed high strength steel in the fluid block.
U.S. Pat. No. 3,786,729 is directed to a liner seal for the plunger bore and does not address the protection of high stress areas such as those associated with intersecting bores.